The established congregation that earns the multiplied reward mentioned in the hadiths is the one that prays with the resident imam or someone who stands in for him, and prays at the preferred time. The imam has the right to perform the prayer at the beginning or end of the preferred time, as the Prophet Muhammad, peace be upon him, used to do.
It is not valid to precede the established congregation with an individual congregation prayer. Instead, people should pray individually if they need to. If they pray in a congregation, their prayer is valid and goes against the Sunnah.
Imam Al-Buhuti Al-Hanbali said: “It is forbidden to lead the prayer in a mosque before the resident imam without his permission, because he is like the owner of the house and has the right to lead. The Prophet, peace be upon him, said: ‘No man should lead another man in his house without his permission.’ This is reported by Muslim. It also leads to the discouragement of the resident imam, and it invalidates the benefit of his position being advanced.”
This is if the mosque has a resident imam. If there is no resident imam, such as in a market or roadside mosque, or if there is no regular imam, then it is permissible to have multiple congregations.
As for the Adhan and repeating it with the repeating of the congregation, there have been differences of opinion among the schools of law:
The Hanafi School of law says that if a mosque has known regular attendees and someone else prays there with a call to prayer and Iqama, it is not disliked to repeat the call to prayer and Iqama.
If the regular attendees or some of them have already prayed with the Adhan and Iqama, it is disliked for non-regular attendees or the rest of its attendees to repeat the Adhan and Iqama.
If the mosque does not have any known regular attendees, such as if it is on a road, then it is not disliked to repeat the Adhan and Iqama in it.
The Shafi’i and Hanbali schools of law permit repeating the Adhan and Iqama as long as the sound does not disturb or confuse people.
The Maliki School of law, on the other hand, considers it disliked to repeat the Adhan not Iqama.
The correct view is that the purpose of the Adhan is to announce the time for prayer, and there is no need for an announcement except when the time for prayer enters. The Iqama is sufficient for them to perform the prayer.
And Allah knows best.
Fatwa by Dr. Khālid Naṣr